Conventional passenger transport aircraft typically include an air conditioning system including one or more air conditioning plants or packs, commonly based on an air cycle process, in which highly compressed process air, namely bleed air from a propulsion engine or an auxiliary power unit (APU) engine, is compressed and expanded, while being cooled by heat exchange at one or more stages. Through this air cycle, the process air is cooled and dehumidified. The cooling of the process air through a heat exchanger during the air cycle may, among other things, be carried out in a main or primary heat exchanger operating as a ram air heat exchanger. In this regard, cooler ambient air from the outside environment surrounding the aircraft flows through one set of passages of this heat exchanger, while removing heat from the hot process air that flows through the other set of passages of this heat exchanger. This cool ambient air is typically ram air entering a ram air intake and flowing through a ram air channel to the main or primary heat exchanger. The ram air intake is typically arranged on the outside fuselage at a location exhibiting an increased ram or stagnation air pressure due to the apparent incident wind of the oncoming air during flight of the aircraft. After passing through the heat exchanger, the ram air is then exhausted through an outlet channel that exits the aircraft fuselage at an area of relatively lower pressure in comparison to the stagnation or ram pressure existing at the ram air intake.
In many conventional aircraft types, the air conditioning packs are installed in the lower portion of the aircraft fuselage, or particularly in the area of the so called “belly fairing”, such as in the Airbus A319, A320, A321, A330 and A340 aircraft. To provide the cooling ram air to the air conditioning packs located in the belly fairing, these aircraft typically include ram air inlets or intake openings in the lower belly area of the aircraft fuselage.
In the planning and construction of aircraft, it is desired or intended to move the air conditioning packs from the location in the belly fairing to a location at the sides of the interior of the fuselage, near the wing roots. Especially with such a location of the air conditioning packs, the previously existing location of ram air inlets is not optimal, for example due to long ram air channels that would be required. There is thus a need to provide an arrangement of ram air inlets at exterior locations of the aircraft subjected to the highest stagnation or ram air pressure of the outside ambient air during flight of the aircraft, while also achieving the shortest and most direct configuration of the ram air channels leading to the air conditioning pack heat exchangers, in order to reduce the overall weight, while increasing the cooling efficiency and the maximum cooling capacity of the air conditioning system. However, on the other hand, a location and configuration of the ram air inlets must ensure that the overall aerodynamic resistance, e.g. the total coefficient of drag, of the aircraft is not significantly increased by these ram air inlets.
It is further known to provide inlet closure flaps for selectively opening or closing the ram air intake openings so as to control the inlet flow of ram air. For example, in the Airbus A320 aircraft, it is known to arrange only a single individual inlet flap in the ram air intake. On the other hand, in the Airbus A330 and A340 aircraft, it is known to provide both an inlet flap and an outlet flap for controlling the flow of the ram air.
It has been found that the existing ram air inlet flap arrangements still leave room for improvement, i.e. for optimizing the airflow control and flow characteristics of the ram air through the air intake channel, as well as the total air resistance or drag generated by the air inlet arrangement in the open position, the closed position, and any intermediate position.